DETAILED DESCRIPTION OF THE INVENTION The novel catalyst systems of the present invention are prepared by depositing, on an inorganic support material having surface hydroxyl groups, aluminum acetylacetonate compound and an organophosphoryl chromium product.
The supported chromium containing product and aluminum compound are then heated in a non-reducing atmosphere at a temperature above about 300.
degree.
C.
up to the decomposition temperature of the support material.
It is believed that the chromium containing product and the aluminum compound react with the surface hydroxyl groups on the inorganic support material during the course of preparing the novel catalyst systems of the present invention.
However, the precise mechanism involved is not known and applicants do not wish to be restricted to the mechanism postulated above.
The inorganic support materials useful in the present invention include those normally employed in supported chromium catalysts used in olefin polymerizations such as those discussed in U.
S.
Pat.
No.
2,825,721.
Typically, these support materials are inorganic oxides of silica, alumina, silica-alumina mixtures, thoria, zirconia and comparable oxides which are porous, have a medium surface area, and have surface hydroxyl groups.
Preferred support materials are silica xerogels or xerogels containing silica as the major constituent.
Especially preferred are the silica xerogels described in U.
S.
Pat.
No.
3,652,214 which silica xerogels have a surface area in the range of 200 to 500 m.
sup.
2 /g, a pore volume greater than about 2.
0 cc/g, a major portion of the pore volume being provided by pores having diameters in the range of 300 to 600 A.
The chromium containing compounds useful in the present invention comprise the organophosphoryl chromium compounds disclosed in applicants U.
S.
Pat.
No.
3,985,676 (incorporated herein by reference) which comprise the reaction product of chromium trioxide with an organophosphorus compound having the formula: ##STR1## wherein R is alkyl, aralkyl, aryl, cycloalkyl or hydrogen, but at least one R is other than hydrogen
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